* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
div {
    /* 多行效果：宽度100%占据一整行，便会自动换行 */
    width: 100%;
    height: 100px;
}

div:nth-child(odd) {
    background-color: skyblue;
}

div:nth-child(even) {
    background-color: orangered;
}